1. Field of the Invention
The present invention generally relates to wellbore tubulars. More particularly, the invention relates to expandable tubulars in a wellbore. More particularly still, the invention relates to apparatus and methods for expanding a first, smaller diameter tubular into frictional contact with a second, larger diameter tubular or wellbore.
2. Description of the Related Art
Operations in a wellbore are typically carried out with a downhole tool mounted at the end of a string of tubulars. Likewise, the transportation of production fluid to a surface of the wellbore is performed using a string of tubulars to form a fluid path. In other instances, tubulars are used to line the wellbore to facilitate the isolation of hydrocarbon bearing formations and support the walls of the wellbore. Therefore, tubulars are strung together to make a long string that can stretch from a lower end of the wellbore to the surface of the wellbore in all these situations.
Recently, expandable tubulars have been introduced that can be enlarged in diameter at a predetermined location in the wellbore. These expandable tubulars have facilitated many wellbore operations and permit a tubular of a smaller diameter to be inserted into the wellbore and subsequently enlarged in-situ. One use for expandable tubulars includes the expansion of a first, smaller diameter tubular into a second, larger diameter tubular to form a seal or frictional relationship there between. The expansion is typically performed using a fluid actuated expander tool which includes one or more radially extendable expanding members which contact the inner wall of the tubular and urge it past its elastic limits. By rotating the expander tool on a work string while the expanding members are actuated, a tubular can be circumferentially expanded into frictional contact with a wellbore or another tubular there around. In this manner, a smaller diameter tubular can be hung in place in a larger diameter tubular without the use of mechanical cones and slips, which utilize valuable real estate in an annular area between tubulars.
There are problems associated with hanging one tubular inside another through expansion. For example, to affect an adequate frictional relationship between the two tubulars, an outer surface of the smaller tubular must be supplied with some type of grip-enhancing material or formations. These formations must be fabricated on the outer surface of the tubular or on a separate sub assembly attached at the top of the tubular, leading to additional expense. Use of these prior art methods has also resulted in inconsistent results, with the tubular sometimes loosing its grip on the wall of the larger tubular due to subsequent operations. Additionally, the provision of hardened formations or buttons to the tubular increases its thickness and makes its expansion more difficult.
Therefore, there exists a need for more effective apparatus and methods of providing an adequate griping surface between a larger tubular and a smaller tubular for expansion into frictional contact with the larger tubular. There is a further need for flexible apparatus and methods for providing grip-enhancing formations on a tubular whereby the formations are easily selected depending upon a particular need.